1. Field of the Invention
The invention relates to a method for charging storage battery packs, in particular NiCd and NiMH battery backs for electrical hand tool machines.
In particular, it must be possible to recharge NiCd and NiMH battery backs for electrical hand tool machines to almost continually use the electrical hand tool by exchanging one battery pack for another. Nonetheless, critical values specific to the battery, in particular the temperature at the time of charging, must be taken into account to obtain an adequate service life of the NiCd battery pack. Associated charger devices usually monitor the temperature of the battery pack by a temperature sensor arranged in the battery pack.
2. Description of the Prior Art
Battery packs comprise a number of cells that are at least partially connected in series with each other. Accordingly, the identical current flows through all of these cells at the time of use and at the time of charging. The usable capacity of a battery pack is consequently determined by the capacity of the weakest cell, which limits the service life of the battery pack. The battery pack must be regularly regenerated in a refresh cycle to obtain the desired increase in capacity, especially of the weakest cell. These type of refresh cycles usually consist of individual refresh cycles and optional refresh discharge cycles using a comparatively low current strength of less than 50% relative to the charging cycle.
According to EP 450 783, a refresh cycle using approximately 100 mA following charging using approximately 700 mA is carried out independently of the charge status of a battery, which can be automatically enabled by the microcontroller in the consumer. According to U.S. Pat. No. 6,191,554, a double charge/discharge of the NiCd battery and update of the data memory arranged in the battery is done in a manually enabled, pre-programmed refresh cycle.
According to U.S. Pat. No. 6,154,008, in a NiCd battery pack for electrical hand tool machines, following temperature—controlled charging at 50° C. for approximately 2 h, a manually enabled refresh cycle enabled by a refresh switch over a period of from 4 to 8 h using a low refresh current effects an overcharge. Especially in the rough construction trades, a refresh in a manually selectable refresh cycle is frequently done too often or inadequately, whereby the possible service life of the battery pack is not attained. In addition, the refresh cycle requires too much time and thus a quasi-continuous utilization is not possible when changing over.